Is your 4gb SDHC?? I have a 2gb for my EZV and it works fine but I'm not sure what the size limit is...
As I understand SDHC needs special...something implimented. The supercard is the first (that I know) to have SDHC capability.

I can't answer your question really....hopefully someone else can!! I'd like to know before I go after a 4gb myself...
IF it isnt supported now...maybe it can be in the future through updates?? Haven't heard much about this...